A fuel cell generates power by supplying a fuel gas to a fuel pole (anode electrode) and an oxidizing gas to an oxidation agent pole (cathode electrode), thereby allowing an electrochemical reaction between the fuel gas and the oxidizing gas. In a fuel cell, a fuel gas supply pipe for supplying the fuel gas to the body of the fuel cell, a fuel gas discharge pipe for discharging the fuel gas from the fuel cell body, an oxidizing gas supply pipe for supplying the oxidizing gas to the fuel cell body, and an oxidizing gas discharge pipe for discharging the oxidizing gas from the fuel cell body are provided. In this specification, these pipes are collectively referred to as a “supply and discharge pipe of reaction gas”. A reaction gas flow path refers to a flow path in the reaction gas pipe through which the reaction gas is circulated.
In a fuel cell such as a solid polymer electrolyte fuel cell (PEFC), normally, an electrolytic membrane comprising a fluorine resin-based ion exchange membrane which is a proton-transmitting structure is sandwiched between an anode and a cathode each comprising a catalyst layer and a gas diffusion layer, to form an MEA (Membrane Electrode Assembly). A fuel gas such as, for example, hydrogen is supplied to the anode side of the MEA, and an oxidizing gas such as, for example, oxygen is supplied to the cathode side of the MEA so that a chemical reaction occurs at the catalyst layers. On the anode side, hydrogen is separated into a proton (H+) and an electron (e−), and the proton moves in the electrolytic membrane with the water molecule. The electron, meanwhile, moves to the cathode side through an external circuit. On the cathode side, the oxygen in the oxidizing agent and the proton and the electron moved from the anode side react, thereby generating water. Therefore, this moisture may flow into the reaction gas supply and discharge pipe.
For the reaction gas containing moisture flowing in the supply and discharge pipe, the temperature of the reaction gas is reduced when a filling pressure of the tank is lowered, according to the Boyle-Charles Law. In addition, when the fuel cell is placed in a low-temperature environment, a cold reaction gas flows. In such a situation, the moisture in the fluid may condensate on a pressure sensor portion or the like and the pressure sensor may be frozen. In particular, when the fuel cell system is stopped and a high-temperature reaction gas does not flow, the moisture may be frozen under the above-described environment.
In the react ion gas supply and discharge pipe, a pressure sensor for measuring the pressure of the reaction gas is provided, and the amount of generated power or the like of the fuel cell body is controlled by adjusting the pressure of the reaction gas. A pressure sensor of the related art comprises an engagement section which is threaded, which engages a pipe wall of a reaction gas pipe, and which is sealed by a seal member, a flange, a housing, a diaphragm which is a pressure-detecting section mounted on the housing, and a displacement sensor which is provided on the diaphragm. In the housing of the pressure sensor, a connecting chamber which is in communication with a reaction gas flow path is provided, and the connecting chamber faces a pressure-receiving surface of the diaphragm. The diaphragm opposes the connecting chamber, and detects the pressure of the reaction gas in the reaction gas pipe through deformation. The displacement sensor to which a terminal is connected measures the displacement of the diaphragm.
A pressure sensor of another example configuration of the related art comprises an engagement section which is threaded, which engages a pipe wall of a reaction gas pipe, and which is sealed by a seal member, a flange, a housing, a diaphragm which serves as a pressure-detecting section mounted on the housing, and a displacement sensor which is provided on the diaphragm. A pressure-receiving surface of the diaphragm faces a reaction gas flow path of the reaction gas pipe. The diaphragm directly detects the pressure of the reaction gas in the reaction gas flow path through deformation. The displacement sensor to which a terminal is connected measures the displacement of the diaphragm.
Meanwhile, JP 2006-162491 A discloses a pressure sensor in which a pressure-receiving surface on a side of a sensor element near the fluid to be measured is covered and sealed with a flexible structure, and an antifreeze agent is filled between the pressure-receiving surface of the sensor element and the flexible structure. JP 2005-164538 A discloses a pressure sensor in which a pressure sensor frost heater is mounted on a pressure sensor mounting boss and the moisture in the pressure sensor is defrosted.